Humans share a similar repertoire of genetic and cellular make-up with the fruit fly Drosophila melanogaster, our long term goal is to use Drosophila as model system to understand the role of ?- secretase in maintaining cell health and how malfunctions of ?-secretase, such as those associated with Familial Alzheimer's Disease (FAD), can affect cell viability and eventually lead to cell death. Our current focus is to investigate how the functioning of Presenilin (Psn) is regulated. Normally Presenilin is the catalytic subunit of the ?-secretase complex that contains another three components, Nicastrin (Nct), Aph-1, and Pen-2, to cleave transmembrane proteins including Notch and amyloid precursor protein (APP). During assembly of the complex, Aph-1, Nct, and Pen-2 assist Psn endoproteolysis to form a Psn-NTF/ Psn-CTF heterodimer that providing the catalytic subunit of ?-secretase. Our previous results suggested that, in addition to regulating the protease activity mediated by the matured Presenilin, cofactors like Aph-1 also regulates cell viability possibly by down regulating the Psn holoprotein. The specific hypothesis behind this proposal is that cofactors of the ?-secretase complex such as Aph-1 and Pen-2 regulate the functions of Presenilin in multiple ways: assisting Psn endoproteolysis, regulating the catalytic activity of the matured Psn, and controlling cell death by preventing the Psn holoprotein from promoting apoptosis. Our specific aims are to investigate whether Pen-2 plays a similar role to Aph-1 in regulating ?-secretase activity (specific aim 1), and to examine how Aph-1 regulates cell viability (specific aims 2 and 3). We will use a series of transgenic flies that we previously established to perform genetic and biochemical studies for this investigation. The answers gained from this in vivo investigation will be very informative to address the role of the ?-secretase complex in controlling cell death in physiological conditions of human cells, hence shedding light on understanding the pathological causes of massive neuronal cell death in brains of neurodegenerative disease patients like FAD patients and on designing proper treatments. PUBLIC HEALTH RELEVANCE: This proposal has an impact on understanding the aging phenomenon and human neurodegenerative diseases like Alzheimer's disease. Therefore it is relevant to the mechanism and policy making of how to care for the population of elderly in our society.